1. Field of the Invention
The present invention relates to an optical disk device for recording a signal to and reading a signal from an optical disk, and a slider control method.
2. Description of the Related Art
Some types of optical disk devices for recording a signal to and reading a signal from the optical disk perform slider follow-up control during a track servo operation so that an objective lens operates in the vicinity of the center of an optical field of view.
A slider is designed to control a pickup in position so that the objective lens driven in a tracking direction is aligned in position with the center of the optical field of view of the pickup.
In the slider follow-up control, a displacement between the objective lens and the center of the optical field of view is estimated from the level of a low-frequency component of a tracking servo signal for a tracking operation.
For example, if a zero level is obtained as the level of the low-frequency component of the tracking servo signal, the objective lens is approximately aligned with a mechanical center position. In a pickup, the center of the optical field of view is set up to be aligned with the vicinity of the mechanical center position of the objective lens.
If the slider control is performed to move the pickup so that the level of the low-frequency component of the track servo signal becomes a zero level, the center of the optical field of view is thus caused to follow the objective lens.
Such an optical disk device is implemented as a video camera. The optical disk device as the video camera is typically carried and used in a variety of angles by a user.
Depending on the direction of the optical disk device, the objective lens may shift down to the tracking direction with the gravity thereof.
As is known, the objective lens is relatively softly supported by an actuator with an arm thereof in the optical disk system. When the optical disk device is tilted, the objective lens is shifted from the mechanical center position in the direction of gravity pull.
If the objective lens is shifted by its own weight in response to a change in the posture of the optical disk device, the slider follow-up control cannot be properly performed.
Even if the low-frequency component of the tracking servo signal is close to the zero level, the objective lens is already shifted from the mechanical center position in the direction of gravity pull with its own weight. If slider control is performed with a track target set to a position where the low-frequency component of the tracking servo signal becomes a zero level, the objective lens is thus shifted from the center of the optical field of view.
If the objective lens is displaced in position from the center of the optical field of view in the slider follow-up control, good optical characteristics cannot be achieved. The optical disk device becomes unstable in the tracking servo operation, and may exhibit poor recording and replay performance.
U.S. Pat. No. 6,473,373 discloses a technique that corrects position displacement of an objective lens in the movable direction thereof.